One of the most efficient methods for making a large display is to use projected images. Conventionally, the most advanced projection systems use imaging devices such as digital micro-mirror (DMD), Liquid Crystal on Silicon (LCoS), or transmissive LCD micro-displays. Typically, one or two fold mirrors are used in projection displays in order to fold the optical path and make a portion of it vertical to reduce the cabinet depth of projection displays. In a single fold mirror rear projection display, the light engine converts digital images to optical images with one or more microdisplays, and then projects the optical image to a large mirror which relays the optical images through a rear projection screen to a viewer in front of the screen. The light engine also manages light colors to yield full color images and magnifies the image. In a two fold mirror rear projection display, the projected optical images from the light engine are reflected off of a first fold mirror to a second fold mirror, and then through the rear projection screen to a viewer. The two fold mirror structure provides additional reduction in TV cabinet depth over one fold mirror structures, but typically requires additional cabinet height below the screen. The height of the cabinet below the screen is called chin height and it grows as the light engine projects to a first fold mirror typically positioned below the screen.
Because the imaging devices in projection displays are small, typically less than 1″ in diagonal, they are inexpensive to manufacture. However, the small images generated by the imaging devices require magnification factors up to 100 in order to yield the 50″-80″ diagonal image typical in consumer projection televisions. This high magnification makes the alignment of optical elements in these projection systems critical to final image quality. If the position of the light engine, the large mirror, and/or small mirror changes relative to the screen, the image quality will suffer. A change in any of the relative relationships between these elements from the nominal design can result in image keystoning or distortion, image rotation or shifting from its best position on the screen, or a loss of image focus. Therefore, special care is taken in manufacturing to insure precise alignment of the display optics.
The depth of these rear projection displays varies with their diagonal size, but with conventional optics the typical ratio of screen diagonal to cabinet depth is 2.5-3.5.:1. Thus, a 70″ diagonal display will be 23″ deep, and a 55″ diagonal display will have a depth of 18.3″. Large projection displays are extremely difficult to handle, expensive to transport, and, because of their size and fragility, their optical alignment can be easily disrupted when they shipped from manufacturer to the dealer or customer, or when moved from room to room in use. Once out of alignment, these displays typically need to be returned to the manufacturer to be realigned, or if that is impractical, the manufacturer pays for an expensive on-site service call. Often, the customer accepts a display with a poor quality image because it is too difficult or expensive to repair. Additionally, because each cabinet configuration must be aligned at the factory, it is impractical for a manufacturer to provide custom display sizes to match a customer's requirements.
Accordingly, a new system and method are needed that overcome the above-mentioned deficiencies in a cost efficient manner.